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C++ 正则表达式例程，C++11 <regex>使用例子，

以下代码使用正则表达式查找给定字符串中，长度大于6个字节的单词。

代码来自 https://en.cppreference.com/w/cpp/regex， 仅做学习用途。

#include <iostream>
#include <iterator>
#include <string>
#include <regex>
 
int main()
{
    std::string s = "Some people, when confronted with a problem, think "
        "\"I know, I'll use regular expressions.\" "
        "Now they have two problems.";
 
    std::regex self_regex("REGULAR EXPRESSIONS",
            std::regex_constants::ECMAScript | std::regex_constants::icase);
    if (std::regex_search(s, self_regex)) {
        std::cout << "Text contains the phrase 'regular expressions'\n";
    }
 
    std::regex word_regex("(\\w+)");
    auto words_begin = 
        std::sregex_iterator(s.begin(), s.end(), word_regex);
    auto words_end = std::sregex_iterator();
 
    std::cout << "Found "
              << std::distance(words_begin, words_end)
              << " words\n";
 
    const int N = 6;
    std::cout << "Words longer than " << N << " characters:\n";
    for (std::sregex_iterator i = words_begin; i != words_end; ++i) {
        std::smatch match = *i;
        std::string match_str = match.str();
        if (match_str.size() > N) {
            std::cout << "  " << match_str << '\n';
        }
    }
 
    std::regex long_word_regex("(\\w{7,})");
    std::string new_s = std::regex_replace(s, long_word_regex, "[$&]");
    std::cout << new_s << '\n';
}

上述例子，GCC 12.1编译执行输出结果如下：（顺便安利一个工具网站，https://godbolt.org/ 可提供在线C++编译浏览，对于临时做轻量代码编译测试是个不错的选择）

ASM generation compiler returned: 0
Execution build compiler returned: 0
Program returned: 0
Text contains the phrase 'regular expressions'
Found 20 words
Words longer than 6 characters:
  confronted
  problem
  regular
  expressions
  problems
Some people, when [confronted] with a [problem], think "I know, I'll use [regular] [expressions]." Now they have two [problems].